Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having negative refractive power, a second lens having negative refractive power, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The first to seventh lenses are sequentially disposed from an object side toward an image side. The third lens and the seventh lens are formed of plastic, and the first lens, the second lens, the fourth lens, the fifth lens, and the sixth lens are formed of glass.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2017-0155623 filed on Nov. 21, 2017, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND 1. Field

This application relates to an optical imaging system.

2. Description of the Background

In general, camera modules are mounted in mobile communicationsterminals, computers, vehicles, and the like, enabling the capturing ofimages.

In accordance with the trend for slimmer mobile communicationsterminals, such camera modules have been required to have a small sizeand high image quality.

Meanwhile, a camera module for a vehicle has also been required to havea small size and high image quality to not obstruct a driver's visualfield and spoil a vehicle appearance.

Particularly, a camera used in a rearview mirror of a vehicle should beable to capture a clear image to secure a rear visual field duringdriving of the vehicle, and is thus required to have high image quality.

In addition, a camera used in a vehicle should be able to clearlycapture an image of an object, even at night when illumination is low,and thus requires a lens system that has a small size and which maycapture an image in both of a visible wavelength region and a nearinfrared region.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system includes a first lenshaving negative refractive power, a second lens having negativerefractive power, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens. The first to seventh lenses are sequentiallydisposed from an object side toward an image side, the third lens andthe seventh lens are formed of plastic, and the first lens, the secondlens, the fourth lens, the fifth lens, and the sixth lens are formed ofglass.

The object-side surfaces and image-side surfaces of the first lens, thesecond lens, the fourth lens, the fifth lens, and the sixth lens may bespherical surfaces, and object-side surfaces and image-side surfaces ofthe third lens and the seventh lens may be aspherical surfaces.

The third lens and the seventh lens may be formed of plastic having thesame optical characteristics as each other.

The fifth lens and the sixth lens may be formed of glass havingdifferent optical characteristics from each other.

The fifth lens and the sixth lens may be cemented to each other.

The optical imaging system may further include a stop disposed betweenthe fourth lens and the fifth lens.

In the optical imaging system TTL is a distance from an object-sidesurface of the first lens to an imaging plane of an image sensor, IMGHis a half of a diagonal length of the imaging plane of the image sensor,and TTL/(2*IMGH) may be less than 3.05.

In the optical imaging system R5 is a radius of curvature of anobject-side surface of the third lens, f is an overall focal length ofthe optical imaging system including the first lens to the seventh lens,and R5/f may be greater than −15.0 and less than −5.0.

In the optical imaging system f3 is a focal length of the third lens andf/f3 may be greater than 0.02 and less than 0.08.

In the optical imaging system f7 is a focal length of the seventh lensand f/f7 may be greater than 0.4 and less than 0.48.

In the optical imaging system n3 is a refractive index of the third lensand n3 may be less than 1.535.

In the optical imaging system n7 is a refractive index of the seventhlens and n7 may be less than 1.535.

In the optical imaging system R1 is a radius of curvature of anobject-side surface of the first lens, R2 is a radius of curvature of animage-side surface of the first lens, and R1/R2 may be greater than 3.5.

In the optical imaging system R3 is a radius of curvature of anobject-side surface of the second lens, R4 is a radius of curvature ofan image-side surface of the second lens, and R3/R4 may be greater than10.

In another general aspect, an optical imaging system includes a firstlens having negative refractive power and having a meniscus shape, ofwhich an object-side surface is convex, a second lens having negativerefractive power and having a meniscus shape, of which an object-sidesurface is convex, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens. The first to seventh lenses are sequentiallydisposed from an object side toward an image side. The third lens andthe seventh lens are formed of plastic. The first lens, the second lens,the fourth lens, the fifth lens, and the sixth lens are formed of glass,and an image-side surface of the fifth lens and an object-side surfaceof the sixth lens are cemented to each other.

The third lens and the seventh lens may each have positive refractivepower.

The third lens may have a concave object-side surface and a conveximage-side surface, and the fourth lens and the seventh lens may eachhave convex object-side and image-side surfaces.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a first example of an optical imagingsystem.

FIG. 2 illustrates examples of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 1.

FIG. 3 is a view illustrating a second example of an optical imagingsystem.

FIG. 4 illustrates examples of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 3.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

In the drawings, the thicknesses, sizes, and shapes of lenses have beenslightly exaggerated for convenience of explanation. Particularly, theshapes of spherical surfaces or aspherical surfaces illustrated in thedrawings are illustrated by way of example. That is, the shapes of thespherical surfaces or the aspherical surfaces are not limited to thoseillustrated in the drawings.

In this application, a first lens refers to a lens closest to an object,while a seventh lens refers to a lens closest to an image sensor.

In addition, a first surface of each lens refers to a surface thereofclosest to an object side (or an object-side surface) and a secondsurface of each lens refers to a surface thereof closest to an imageside (or an image-side surface). Further, all numerical values of radiiof curvature and thicknesses of lenses, image heights (ImgH, a half of adiagonal length of an imaging plane of the image sensor), and the like,are indicated by millimeters (mm), and a field of view (FOV) of anoptical imaging system is indicated by degrees.

Further, in a description for a shape of each of the lenses, the meaningthat one surface of a lens is convex is that a paraxial region portionof a corresponding surface is convex, and the meaning that one surfaceof a lens is concave is that a paraxial region portion of acorresponding surface is concave. Therefore, although it is describedthat one surface of a lens is convex, an edge portion of the lens may beconcave. Likewise, although it is described that one surface of a lensis concave, an edge portion of the lens may be convex.

A paraxial region refers to a very narrow region in the vicinity of anoptical axis.

An aspect of the present disclosure provides an optical imaging systemin which an aberration improvement effect may be increased, a high levelof resolution may be implemented, imaging may be performed even in anenvironment in which illumination is low, and a deviation in resolutionmay be suppressed even over a wide change in temperature.

An optical imaging system in the examples described herein may includeseven lenses.

For example, the optical imaging system may include a first lens, asecond lens, a third lens, a fourth lens, a fifth lens, a sixth lens,and a seventh lens sequentially disposed from the object side.

However, the optical imaging system is not limited to only including theseven lenses, but may further include other components, if necessary.

For example, the optical imaging system may further include an imagesensor configured to convert an image of a subject incident on the imagesensor into an electrical signal. The image sensor may be configured tocapture an image of an object in a near infrared region as well as avisible light region.

In addition, the optical imaging system may further include a stopconfigured to control an amount of light. For example, the stop may bedisposed between the fourth and fifth lenses.

In the optical imaging system in the examples described herein, some ofthe first to seventh lenses may be formed of plastic, and the othersthereof may be formed of glass. In addition, the lenses formed of glassmay have optical characteristics different from those of the lensesformed of plastic.

For example, the first lens, the second lens, the fourth lens, the fifthlens, and the sixth lens may be formed of glass, and the third lens andthe seventh lens may be formed of plastic.

In addition, in the optical imaging system in the examples describedherein, some of the first to seventh lenses may be aspherical lenses,and the others thereof may be spherical lenses.

As an example, first surfaces and second surfaces of the first lens, thesecond lens, the fourth lens, the fifth lens, and the sixth lens may bespherical surfaces, and first surfaces and second surfaces of the thirdlens and the seventh lens may be aspherical surfaces.

The aspherical surfaces of the third lens and the seventh lens may berepresented by the following Equation 1:

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10} + {EY}^{12} + {FY}^{14} + \ldots}} & (1)\end{matrix}$

In Equation 1, c is a curvature (an inverse of a radius of curvature) ofa lens, K is a conic constant, and Y is a distance from a certain pointon an aspherical surface of the lens to an optical axis in a directionperpendicular to the optical axis. In addition, constants A to F areaspherical coefficients. In addition, Z is a distance between thecertain point on the aspherical surface of the lens at the distance Yand a tangential plane meeting the apex of the aspherical surface of thelens.

The optical imaging system including the first to seventh lenses mayhave negative refractive power/negative refractive power/positiverefractive power/positive refractive power/positive refractivepower/negative refractive power/positive refractive power sequentiallyfrom the object side.

The optical imaging system in the examples described herein may satisfythe following Conditional Expressions 2 through 9:TTL/(2*IMGH)<3.05  (2)−15.0<R5/f<−5.0  (3)0.02<f/f3<0.08  (4)0.4<f/f7<0.48  (5)n3<1.535  (6)n7<1.535  (7)R1/R2>3.5  (8)R3/R4>10  (9)

In the above Conditional Expressions 2 through 9, TTL is a distance froman object-side surface of the first lens to the imaging plane of theimage sensor, IMGH is a half of a diagonal length of the imaging planeof the image sensor, R5 is a radius of curvature of an object-sidesurface of the third lens, f is an overall focal length of the opticalimaging system, f3 is a focal length of the third lens, f7 is a focallength of the seventh lens, n3 is a refractive index of the third lens,n7 is a refractive index of the seventh lens, R1 is a radius ofcurvature of an object-side surface of the first lens, R2 is a radius ofcurvature of an image-side surface of the first lens, R3 is a radius ofcurvature of an object-side surface of the second lens, and R4 is aradius of curvature of an image-side surface of the second lens.

Next, the first to seventh lenses constituting the optical imagingsystem in some examples will be described.

The first lens may have negative refractive power. In addition, thefirst lens may have a meniscus shape, of which an object-side surface isconvex. In detail, a first surface of the first lens may be convex inthe paraxial region, and a second surface thereof may be concave in theparaxial region.

Both surfaces of the first lens may be spherical surfaces.

The second lens may have negative refractive power. In addition, thesecond lens may have a meniscus shape, of which an object-side surfaceis convex. In detail, a first surface of the second lens may be convexin the paraxial region, and a second surface thereof may be concave inthe paraxial region.

Both surfaces of the second lens may be spherical surfaces.

The third lens may have positive refractive power. In addition, thethird lens may have a meniscus shape of which an image-side surface isconvex. In detail, a first surface of the third lens may be concave inthe paraxial region, and a second surface thereof may be convex in theparaxial region.

Both surfaces of the third lens may be aspherical surfaces.

The fourth lens may have positive refractive power. In addition, bothsurfaces of the fourth lens may be convex. In detail, first and secondsurfaces of the fourth lens may be convex in the paraxial region.

Both surfaces of the fourth lens may be spherical surfaces.

The fifth lens may have positive refractive power. In addition, bothsurfaces of the fifth lens may be convex. In detail, first and secondsurfaces of the fifth lens may be convex in the paraxial region.

Both surfaces of the fifth lens may be spherical surfaces.

The sixth lens may have negative refractive power. In addition, bothsurfaces of the sixth lens may be concave. In detail, first and secondsurfaces of the sixth lens may be concave in the paraxial region.

Both surfaces of the sixth lens may be spherical surfaces.

Meanwhile, the fifth lens and the sixth lens may be configured as acemented lens. As an example, an image-side surface of the fifth lensand an object-side surface of the sixth lens may be cemented to eachother.

The seventh lens may have positive refractive power. In addition, bothsurfaces of the seventh lens may be convex. In detail, first and secondsurfaces of the seventh lens may be convex in the paraxial region.

Both surfaces of the seventh lens may be aspherical surfaces.

In the optical imaging system configured as described above, a pluralityof lenses may perform an aberration correction function to thus increaseaberration improvement performance.

In addition, the optical imaging system may have an f-number (Fno) (aconstant indicating brightness of the optical imaging system) of 2.4 orless to thus clearly capture an image of an object even in anenvironment in which illumination is low.

In addition, the optical imaging system may clearly capture the image ofthe object in both of a visible light region and a near infrared region.

Further, in the optical imaging system in some of the examples describedherein, the first lens, the second lens, the fourth lens, the fifthlens, and the sixth lens may be configured as spherical lenses to thusreduce costs for manufacturing the optical imaging system.

In addition, in the optical imaging system in some of the examplesdescribed herein, since the first lens, the second lens, the fourthlens, the fifth lens, and the sixth lens are formed of glass having arelatively small coefficient of thermal expansion and the third lens andthe seventh lens are formed of plastic, a constant resolution may bemaintained even over a temperature range of about −40 to about 80° C.Therefore, the optical imaging system in some of the examples describedherein may implement a high level of resolution even in an environmentin which a temperature changes over a wide range.

A housing in which the first lens to the seventh lens are disposed maybe formed of plastic, and the housing may shrink or expand according toa change in temperature of the surrounding environment. Therefore, adistance between the seventh lens and the image sensor may be changed bythe deformation of the housing according to the change in temperature,which may result in a problem that a focus does not converge properly.

However, in the optical imaging system in some of the examples describedherein, since the third lens and the seventh lens are formed of plastic,the third lens and the seventh lens may shrink or expand according tothe change in temperature of the surrounding environment.

Therefore, by designing an amount of deformation of the third lens andthe seventh lens in consideration of an amount of shape deformation ofthe housing according to the change in temperature, a focus position maynot be changed even in a case in which the temperature is changed.

That is, the optical imaging system in some of the examples describedherein may be configured so that a variation of the distance between theseventh lens and the image sensor according to the change in temperaturecorresponds to a variation of the focus position according to the changein temperature.

An optical imaging system according to a first example disclosed hereinwill be described with reference to FIGS. 1 and 2.

The optical imaging system according to the first example may include anoptical system including a first lens 110, a second lens 120, a thirdlens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and aseventh lens 170, and may further include a stop ST, an optical filter180, and an image sensor 190.

Lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe numbers) ofeach lens are shown in Table 1.

TABLE 1 f = 2.24, Fno = 2.32, FOV = 194° Surface Radius of Thickness orRefractive Abbe No. Curvature Distance Index Number Object InfinityInfinity  1 First Lens 13 0.7 1.7725 49.6  2 3.3 2.1356  3 Second Lens28.8197 0.5 1.5891 61.2  4 2.3418 1.5235  5* Third Lens −16.5 1.8 1.531155.7  6* −9.5605 0.1  7 Fourth Lens 8.4557 2.2 1.5174 52.1  8 −3.8111 0 9 Stop Infinity 1.8487 10 Fifth Lens 5.0173 2.6 1.5891 61.2 11 SixthLens −3 0.48 1.8051 25.4 12 5.3655 0.2453  13* Seventh Lens 4.371 3.02121.5311 55.7  14* −5.3017 1.2788 15 Optical Filter Infinity 0.8 1.516764.1 16 Infinity 0.7625 17 Imaging Plane Infinity 0

In surface numbers of Table 1, the notation * indicates an asphericalsurface.

In the first example, the first lens 110 may have negative refractivepower, and a first surface thereof may be convex in the paraxial regionand a second surface thereof may be concave in the paraxial region.

The second lens 120 may have negative refractive power, and a firstsurface thereof may be convex in a paraxial region and a second surfacethereof may be concave in the paraxial region.

The third lens 130 may have positive refractive power, and a firstsurface thereof may be concave in the paraxial region and a secondsurface thereof may be convex in the paraxial region.

The fourth lens 140 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

The fifth lens 150 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

The sixth lens 160 may have negative refractive power, and a firstsurface and a second surface thereof may be concave in the paraxialregion.

The seventh lens 170 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

Meanwhile, respective surfaces of the third lens 130 and the seventhlens 170 may have aspherical coefficients as illustrated in Table 2.

TABLE 2 Surface No. K A B C D 5 −0.01028 −0.00475 0.000166 −9.8E−051.12E−05 6 −0.18758 −0.00073 0.000548 −0.00011  2.4E−05 13 −0.78800−0.00539 0.000305 −1.3E−05 2.65E−07 14 −5.95155 −0.00404 0.00019−9.1E−06 6.75E−08

In addition, the first lens 110, the second lens 120, the fourth lens140, the fifth lens 150, and the sixth lens 160 may be spherical lensesand may be formed of glass. The third lens 130 and the seventh lens 170may be aspherical lenses and may be formed of plastic.

In addition, the third lens 130 and the seventh lens 170 may be formedof plastic having the same optical characteristics as each other.

Meanwhile, the fifth lens 150 and the sixth lens 160 may be configuredas a cemented lens. That is, the fifth lens 150 and the sixth lens 160may be cemented (bonded) to each other. For example, the image-sidesurface of the fifth lens 150 may be cemented to the object-side surfaceof the sixth lens 160. The fifth lens 150 and the sixth lens 160 may beformed of glass having different optical characteristics from eachother.

The fifth lens 150 and the sixth lens 160 formed of glass havingdifferent optical characteristics may be configured as a cemented lensto thus improve chromatic aberration correction performance.

In addition, the stop ST may be disposed in front of the cemented lens.As an example, the stop ST may be disposed between the fourth lens 140and the fifth lens 150.

In addition, the optical imaging system configured as described abovemay have aberration characteristics illustrated in FIG. 2.

An optical imaging system according to a second example disclosed hereinwill be described with reference to FIGS. 3 and 4.

The optical imaging system according to the second example may includean optical system including a first lens 210, a second lens 220, a thirdlens 230, a fourth lens 240, a fifth lens 250, a sixth lens 260, and aseventh lens 270, and may further include a stop ST, an optical filter280, and an image sensor 290.

Lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe numbers) ofeach lens are shown in Table 3.

TABLE 3 f = 2.26, Fno = 2.39, FOV = 194° Surface Radius of Thickness orRefractive Abbe No. Curvature Distance Index Number Object InfinityInfinity  1 First Lens 13 0.7 1.7725 49.6  2 3.3 2.0693  3 Second Lens22.5039 0.5 1.5891 61.2  4 2.2340 1.4852  5* Third Lens −27.6196 1.81.5311 55.7  6* −14.0930 0.1  7 Fourth Lens 7.3398 2.2 1.5174 52.1  8−3.8150 0  9 Stop Infinity 1.7642 10 Fifth Lens 5.0089 2.6 1.5891 61.211 Sixth Lens −3 0.48 1.8051 25.4 12 5.7104 0.1474  13* Seventh Lens4.4845 2.7390 1.5311 55.7  14* −5.8624 1.4043 15 Optical Filter Infinity0.8 1.5167 64.1 16 Infinity 0.8728 17 Imaging Plane Infinity 0

In surface numbers of Table 3, the notation * indicates an asphericalsurface.

In the second example, the first lens 210 may have negative refractivepower, and a first surface thereof may be convex in the paraxial regionand a second surface thereof may be concave in the paraxial region.

The second lens 220 may have negative refractive power, and a firstsurface thereof may be convex in a paraxial region and a second surfacethereof may be concave in the paraxial region.

The third lens 230 may have positive refractive power, and a firstsurface thereof may be concave in the paraxial region and a secondsurface thereof may be convex in the paraxial region.

The fourth lens 240 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

The fifth lens 250 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

The sixth lens 260 may have negative refractive power, and a firstsurface and a second surface thereof may be concave in the paraxialregion.

The seventh lens 270 may have positive refractive power, and a firstsurface and a second surface thereof may be convex in the paraxialregion.

Meanwhile, respective first and second surfaces of the third lens 230and the seventh lens 270 may have aspherical coefficients as illustratedin Table 4.

TABLE 4 Surface No. K A B C D 5 94.32793 −0.00277 0.000518 −0.000213.60E−05 6 6.676489 0.000536 0.000343 −6.72E−05 1.84E−05 13 −1.34768−0.00615 0.000573 −9.07E−05 6.00E−06 14 −14.2459 −0.00876 0.000907−8.55E−05 2.68E−06

In addition, the first lens 210, the second lens 220, the fourth lens240, the fifth lens 250, and the sixth lens 260 may be spherical lensesand may be formed of glass. The third lens 230 and the seventh lens 270may be aspherical lenses and may be formed of plastic.

In addition, the third lens 230 and the seventh lens 270 may be formedof plastic having the same optical characteristics as each other.

Meanwhile, the fifth lens 250 and the sixth lens 260 may be configuredas a cemented lens. The fifth lens 250 and the sixth lens 260 may beformed of glass having different optical characteristics from eachother.

The fifth lens 250 and the sixth lens 260 formed of glass havingdifferent optical characteristics may be configured as the cemented lensto thus improve chromatic aberration correction performance.

In addition, the stop ST may be disposed in the front of the cementedlens. As an example, the stop ST may be disposed between the fourth lens240 and the fifth lens 250.

In addition, the optical imaging system configured as described abovemay have aberration characteristics illustrated in FIG. 4.

As set forth above, in the optical imaging systems in the examplesdisclosed herein, an aberration improvement effect may be increased, ahigh level of resolution may be implemented, imaging may be performedeven in an environment in which illumination is low, and a deviation inresolution may be suppressed even over a wide change in temperature.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system comprising: a firstlens comprising negative refractive power; a second lens comprisingnegative refractive power; a third lens comprising positive refractivepower, and comprising a concave object-side surface and a conveximage-side surface; a fourth lens comprising positive refractive power,and comprising a convex object-side surface and a convex image-sidesurface; a fifth lens comprising positive refractive power, andcomprising a convex object-side surface and a convex image-side surface;a sixth lens comprising negative refractive power, and comprising aconcave object-side surface and a concave image-side surface; and aseventh lens comprising positive refractive power, wherein the opticalimaging system comprises a total of seven lenses and the first toseventh lenses are sequentially disposed from an object side toward animage side such that the fifth lens is spaced apart from the fourth lensat an optical axis, wherein the third lens and the seventh lens areformed of plastic, wherein the first lens, the second lens, the fourthlens, the fifth lens, and the sixth lens are formed of glass, andwherein TTL is a distance from an object-side surface of the first lensto an imaging plane of an image sensor, IMGH is a half of a diagonallength of the imaging plane of the image sensor, and TTL/(2*IMGH)<3.05.2. The optical imaging system of claim 1, wherein object-side surfacesand image-side surfaces of the first lens, the second lens, the fourthlens, the fifth lens, and the sixth lens are spherical surfaces, andobject-side surfaces and image-side surfaces of the third lens and theseventh lens are aspherical surfaces.
 3. The optical imaging system ofclaim 1, wherein the third lens and the seventh lens are formed ofplastic having the same optical characteristics as each other.
 4. Theoptical imaging system of claim 1, wherein the fifth lens and the sixthlens are formed of glass having different optical characteristics fromeach other.
 5. The optical imaging system of claim 4, wherein the fifthlens and the sixth lens are cemented to each other.
 6. The opticalimaging system of claim 1, further comprising a stop disposed betweenthe fourth lens and the fifth lens.
 7. The optical imaging system ofclaim 1, wherein R5 is a radius of curvature of an object-side surfaceof the third lens, f is an overall focal length of the optical imagingsystem including the first lens to the seventh lens, and−15.0<R5/f<−5.0.
 8. The optical imaging system of claim 1, wherein f3 isa focal length of the third lens, f is an overall focal length of theoptical imaging system including the first lens to the seventh lens, and0.02<f/f3<0.08.
 9. The optical imaging system of claim 1, wherein f7 isa focal length of the seventh lens, f is an overall focal length of theoptical imaging system including the first lens to the seventh lens, and0.4<f/f7<0.48.
 10. The optical imaging system of claim 1, wherein n3 isa refractive index of the third lens and n3<1.535.
 11. The opticalimaging system of claim 1, wherein n7 is a refractive index of theseventh lens and n7<1.535.
 12. The optical imaging system of claim 1,wherein R1 is a radius of curvature of an object-side surface of thefirst lens, R2 is a radius of curvature of an image-side surface of thefirst lens, and R1/R2>3.5.
 13. The optical imaging system of claim 1,wherein R3 is a radius of curvature of an object-side surface of thesecond lens, R4 is a radius of curvature of an image-side surface of thesecond lens, and R3/R4>10.
 14. An optical imaging system comprising: afirst lens comprising negative refractive power and having a meniscusshape, of which an object-side surface is convex; a second lenscomprising negative refractive power and having a meniscus shape, ofwhich an object-side surface is convex; a third lens comprising positiverefractive power, and comprising a concave object-side surface and aconvex image-side surface; a fourth lens comprising positive refractivepower, and comprising a convex object-side surface and a conveximage-side surface; a fifth lens comprising positive refractive power,and comprising a convex object-side surface and a convex image-sidesurface; a sixth lens comprising negative refractive power, andcomprising a concave object-side surface and a concave image-sidesurface; and a seventh lens comprising positive refractive power,wherein the optical imaging system comprises a total of seven lenses andthe first to seventh lenses are sequentially disposed from an objectside toward an image side such that the fifth lens is spaced apart fromthe fourth lens at an optical axis, wherein the third lens and theseventh lens are formed of plastic, wherein the first lens, the secondlens, the fourth lens, the fifth lens, and the sixth lens are formed ofglass, wherein an image-side surface of the fifth lens and anobject-side surface of the sixth lens are cemented to each other, andwherein f3 is a focal length of the third lens, f is an overall focallength of the optical imaging system including the first lens to theseventh lens, and 0.02<f/f3<0.08.
 15. The optical imaging system ofclaim 14, wherein R1 is a radius of curvature of an object-side surfaceof the first lens, R2 is a radius of curvature of an image-side surfaceof the first lens, R3 is a radius of curvature of an object-side surfaceof the second lens, R4 is a radius of curvature of an image-side surfaceof the second lens, and R1/R2>3.5 and R3/R4>10.
 16. The optical imagingsystem of claim 14, wherein object-side surfaces and image-side surfacesof the third lens and the seventh lens are aspherical surfaces.
 17. Theoptical imaging system of claim 14, wherein the seventh lens comprisesconvex object-side and image-side surfaces.
 18. The optical imagingsystem of claim 14, wherein object-side surfaces and image-side surfacesof the first lens, the second lens, the fourth lens, the fifth lens, andthe sixth lens are spherical surfaces.